Bones support the body and allow for movement while protecting internal organs. They are made mostly of collagen, a protein, and calcium, a mineral, which provides structure and hardness. There are four types of bones - long, short, flat, and irregular. The 206 bones in the adult human skeleton are divided into the axial skeleton, including the skull, rib cage and tailbone, and the appendicular skeleton, consisting of the shoulder and hip girdles, and leg and arm bones.